Edible fats are emulsified with water-phases to form edible spreads. In margarine and other non-dairy spread production, formation of the emulsion is accomplished by cooling and working of a process stream containing both fat and water. It is commonplace to pasteurize this process stream before cooling and working.
While fat and water are the principal components of edible spreads other components (such as emulsifiers, thickeners, preservatives and anti-spattering agents), as are mentioned below, are included in product formulations to manipulate product properties both in the final product and during processing.
It is commonplace to use "Votator" (RTM) units to work and cool the process stream in edible fat processing. These Votator units include two distinct types of units known as "A-units" and "C-units".
A-units, which are scraped-surface heat-exchangers, serve both to cool and crystallize an emulsion. C-units, which are pin-stirrers, are also used for crystallization but can apply sufficient shear to induce phase inversion of a oil in water emulsion or transformation of a premix to a water-in-oil dispersion. In spread manufacture by the phase-inversion process, it is commonplace to separate the cooling and inversion steps, such that cooling occurs in one or more A-units in line, prior to a C-unit which functions as a phase invertor; thereby converting an oil-in-water process stream to a water-in-oil spread.
Spreads are characterized by a wide range of physical product properties and organoleptic properties. Some of these properties are more important than others in consumer acceptance. In particular, good spreadability, keepability at ambient temperature, second place keepability consistency both at storage and room temperature, mouth meltdown and oil-retention are important properties.
Keepability is known to be influenced by the water droplet distribution and water phase contents. Coarse emulsions containing bacterial and mold nutrients, such as proteins, generally have poor keepability. Fine emulsions are resistant to bacterial spoilage but are still succeptable to mold growth. Water phase distribution is influenced by processing conditions. Keepability can be improved markedly by cold-distribution and cold-storage, but this is not always practical.
Keepability can also be improved by reducing the nutrient content or incorporating microbial growth inhibitors (such as salts and/or acids) in the product. However, reduction of protein content generally results in poor organoleptic properties and can influence processability of the emulsion. The use of preservatives, particularly substances such as potassium sorbate is commonplace, but is not acceptable to some groups of consumers. While it is therefore known that both product composition and process conditions can influence the water-phase distribution, limited success has been enjoyed in the search for a combination of process conditions and product components which enable the manufacture of acceptable products of high physical and microbiological stability but with a very simple formulation.
While fat and water are the principal components of edible spreads, other components (such as emulsifiers, thickeners, preservatives and anti-spattering agents), as are mentioned below, are included in product formulations to manipulate product properties both in the final product and during processing. The first cooling and shearing unit is preferably at least one scraped surface heat exchanger, preferably an "A-unit" for cooling the process stream to the homogenizer input temperature and forming a fat-continuous emulsion with low but non-zero solids content. It is believed that the presence of the cooling and shearing unit is important to ensure that the feed into the homogenizer is fat-continuous and contains a small amount of solid fat.
Preferably the homogenizer means comprise a two step in line homogenizer. It is convenient that the homogenizer should include a high pressure pump. We have found that an "APV Gaulin 300 series two step homogenizer" is suitable although a booster pump may be needed to supply product if the homogenizer is alone incapable of drawing the feedstock from a source. A minor advantage of using a homogenizer with a high pressure pump is that no dosing pump is required.
As a first alternative a homogenizer valve may be employed, "in line".
As a second alternative other homogenizer means such as Jet or other high speed mixers may be employed. The object of the homogenizer means being to prepare a fine emulsion and the apparatus employed not being limited to the homogenizer per se.